Removal of water-insoluble Sudan dyes by Shewanella oneidensis MR-1

► First report on reduction of water-insoluble Sudan azo dyes by Shewanella strains. ► Major activities for Sudan I reduction were found in membranous proteins. ► Quinone electron shuttle stimulated the reduction of Sudan I. Decolorization of water-insoluble Sudan dyes was studied with Shewanella oneidensis MR-1, which removed 66.8%, 43.4%, 56.0% and 33.7% Sudan I–IV in 104h, respectively and reduced Sudan I to aniline and 1-amino-2-naphthol. Lactate was identified as the most efficient electron donor for Sudan I reduction. Improved reduction performance was obtained in the presence of higher lactate or biomass concentration. The correlation between specific reduction rate and initial Sudan I concentration could be described with Michaelis–Menten kinetics (Vmax=1.8mg Sudan Imgcell−1h−1 and Km=5.3mgl−1). The addition of anthraquinone-2-sulfonate stimulated the reduction significantly whereas the presence of 2-hydroxy-1,4-naphthoquinone had little enhancing effect. The main azoreductase activity was found with membrane-bound proteins of MR-1 and no reduction occurred when Sudan I was incubated with cell extracts. These data indicated for the first time that Shewanella could reduce solid-phase Sudan dye particles.